This invention relates to modules for screening particulate material by size, or for diverting the particulate material, to methods of producing such particulate material screening systems, and to reinforcing support frames for such screening modules.
Various modes for connecting a screening module to an underlying frame to form a screening deck are known in the prior art. Some methods require spacers or adapter bars between the screening module and the deck support structure. An example of such an arrangement is shown in U.S. Pat. No. 4,409,099 (“the '099 patent”). The '099 patent shows screening modules supported only at their corners on spacer modules so that the screening element is spaced above the support structure, ostensibly to increase the effective screening area. The intermediate spacer elements, however, add considerably to the cost and complexity of the screening apparatus and increase its overall height. In addition, in order to reduce abrasion by the sifted particulate material to the support structure members, the support members must be specially formed. That requirement represents another expensive departure from standard practices in the industry.
Another screening apparatus that employs specialized components to intermediate the screening elements and the support structure is shown in U.S. Pat. No. 4,219,412 (“the '412 patent”). There, a molded plastic support frame is adapted to receive individual screening elements. The plastic frame, in turn, is connected to the deck support bars. This combination leads to several disadvantages similar to the device of the '099 patent mentioned above. The '412 patent does not disclose whether or how individual screening modules might be removed and replaced.
Similarly, U.S. Pat. No. 4,661,245 (“the '245 patent”) shows a screening system that incorporates clamping bars which receive the individual screening elements. The clamping bars, in turn, are bolted onto the support bars. The resulting structure is unduly complex, expensive, and increases the height of the deck, among other shortcomings.
Several other methods are known for connecting flat screening elements directly to a supporting frame, thereby avoiding the use of spacers or adapter bars. One such method uses a depending hook or skirt member integrally formed in the outlet side of the screening element. An example is shown in U.S. Pat. No. 3,980,555 (“the '555 patent”). In the '555 patent, depending hooks of abutting screening elements are inserted into a frame member through a common mounting hole. The hooks extend out of the mounting hole in the underside of the frame and engage the frame member to hold the screening elements in place. The resulting screening deck has a substantially contiguous inlet surface that provides no access to the mounting hooks for disconnecting an element which requires replacement. Accordingly, such arrangement requires a user to climb under a screening deck and cut the depending hooks off of a module to be replaced. Or, more commonly, a user will pry the element off from the top (inlet side) and destroy it in the process. Either way, the module is rendered useless; a result that is acceptable for modules which are worn out, but wasteful if the module is being replaced merely to change sieve size.
Another attachment method is shown in the '412 patent, discussed above. Individual screening elements are connected to an intermediate supporting frame by integrally formed depending hook-shaped members, similar to those disclosed in the '555 patent. The depending hook members are inaccessible even from the outlet side of the screen, however, as they are enclosed within elongate U-shaped channels. The '412 patent does not disclose any way of removing an individual screening element for replacement, short of disassembling the screening deck.
Another method of connecting screening elements to an underlying frame is to employ securing pins as suggested, for example, in U.S. Pat. No. 4,141,821 (“the '821 patent”). According to the '821 patent, abutting screening elements each include hollow tubular protrusions extending through a common mounting aperture formed in the frame so as to define a hollow tube. A securing pin is inserted into the tube from the inlet side of the deck to spread the protrusions apart beneath the aperture and thereby engage the frame. The securing pin is difficult to pry out of the tube from the inlet side of the screen, although the pin could, perhaps, be driven out from the outlet side of the screen. In any event, once removed, the pin is loose and therefore subject to loss. This is a decided risk in the context of screening machines, as it often is impractical or impossible to retrieve an errant securing pin. A similar securing pin is employed in the apparatus disclosed in the '099 patent discussed previously.
An improved screening system developed by the common assignee of this patent application is provided in U.S. Pat. No. 5,049,262 (“the '262 patent”). The screening system disclosed in the '262 patent includes a rigid frame and a plurality of screening modules. A lock pin is provided which detachably connects the screening modules to the rigid frame. The lock pin is designed so that it remains connected to the frame while allowing removal of the screening modules from the frame, and positioning of a replacement screening module on the frame.
Yet another apparatus for removably mounting screening elements is disclosed in U.S. Pat. No. 4,670,136 (“the '136 patent”). The '136 patent discloses a two-piece elongate clamping element for clamping the edge of a plastic module or wire mesh screen. The apparatus includes a first, lower plastic profile fastened to the load-bearing substructure and arranged to engage under the edges of at least two mutually adjacent screen elements. A second, upper profile is detachably fastened over the first lower profile for retaining the screen elements clamped in place. Removal of a screening element requires removal of the upper plastic profile, thereby subjecting it to risk of loss like the securing pins of the '821 patent and the like. Additionally, the clamping structures of the '136 patent extend substantially beyond the edges of the frame, thereby reducing the effective screening area and subjecting the clamping structure itself to excessive wear from abrasion by particulate material being screened.
Another class of modular screen systems is represented by European Patent No. 167,999 (“EP '999”) and DE 3606-854 (“DE '854”). More specifically, EP '999 is directed to a modular screen system which includes an assembly for attaching sieve elements to a metal support girder. The attachment assembly comprises upper and lower profile sections, and a protective ledge. The upper profile section engages the entire side portion of the sieve elements, while the lower profile section is connected within a continuous slot in the metal support girder. The upper profile can have a bolt-shaped cross-sectional configuration. The protective ledge covers the entire top surface of the support girder to prevent wear from abrasive material passing through the sieve elements. Since the upper profile section is in locking engagement with the entire extent of the side of the sieve element, it is extremely difficult and time consuming for users to remove and replace individual damaged screen modules. Furthermore, this removal process often results in unwanted destruction of adjacent undamaged screen modules.
U.S. Pat. No. 4,674,251 (“the '251 patent”) is directed to a screen component for use in modular screening decks. The screen comprises a frame-shaped molding which surrounds one or more fields having screening openings. At least two of the opposite sides of the molding have supporting members with fastening elements between which reinforcement rods are embedded in the molding extends. Premolding inserts are also embedded in the supporting members and have insert openings on the sides of the inserts facing each other, into which the ends of the reinforcement rods are inserted.
U.S. Pat. No. 5,372,261 (“the '261 patent”) and the '262 patent each relate to a system for screening particulate materials including replaceable screening modules mounted to a rigid frame by lock pins. An internal rigid frame member is typically provided within the module to stiffen it and prevent deformation thereof in the flow direction caused by the weight of particulate material. The lock pins are interlockingly engaged within attachment apertures of the modules.
U.S. Pat. No. 5,377,846 (“the '846 patent”) relates to a screen system having screen panel modules supported side-by-side and/or end-to-end by a support structure assembly. The reinforced renditions of these modules are typically strengthened using a discrete reinforcing bar located therein.
U.S. Pat. No. 5,755,334 (“the '334 patent”) describes an apparatus for mounting a panel on a rail member. Reinforced panels of the '334 patent also include discrete internal reinforcing members.
All of the patents cited above are incorporated in their entirety and by this reference made a part hereof.
In prior art systems when a screening module has become worn out and must be replaced, the old module must be disposed of and preferably recycled. Many reinforced screening modules of the prior art, however, have various types and configurations of discrete internal reinforcing members, which can cause a substantial recycling problem. For example, those screening modules having an internal reinforcing member are much more difficult and costly to dispose of than screening modules formed of two very different materials of constructions, for example, a polymeric module panel and a metal reinforcing member, which undergo different recycling processes. Therefore, the polymeric material portion of the reinforcing member must be separated from the metallic frame before recycling. Unfortunately, the metallic reinforcement is difficult to separate from the remaining polymeric portion of the screening module panel. This means that any recycling process for the above-described reinforced module will be time consuming and expensive.
Additionally, prior art screening polymeric modules having metallic reinforcement must be replaced in their entirety when the polymeric material becomes worn. There is no practical way to replace the polymeric material without also replacing the metallic reinforcing member, even though the reinforcing member can have a substantially longer useful life.
It is important that modules are readily secured during use to a deck assembly but can be easily removed therefrom when repair or replacement of a module is required. Both of these requirements are needed in order to provide maximum functionality of the system.
Accordingly, there remains a need for a particulate screening or diverting module which avoids the problems and meets the needs described above.